1. Field of the Invention
The present invention relates in general to apparatus for recording a video signal and, particularly, to portable apparatus having an image sensor, signal processor, and recorder that may be utilized as a recording video camera.
2. Description of the Prior Art
Video tape recorders (VTR) for home use are now very popular, and these video tape recorders employ a magnetic tape wrapped around a tape guide drum at a specified wrap angle that is slightly greater than 180.degree. and which defines a corresponding circumferential distance around the drum. Two rotary heads, which are spaced 180.degree. apart on the guide drum, are rotated at a known frame frequency and the rotary heads alternately contact the magnetic tape that is being driven at a fixed speed. A video signal to be recorded is fed to the head that is in contact with the tape. In a typical video tape recorder, the fields of a video signal are recorded as obliquely on the magnetic tape. In order to reproduce the video signal this series of tracks, each containing one video field, are scanned by two rotary heads, which are the same as those used in the recording mode.
In a conventional video tape recorder intended for home use, the same unit is used to record as well as to reproduce video signals, however, it has become evident that a very useful piece of equipment would be a portable television camera integrated with a small, light-weight video tape recorder. This unit could be used to make video recordings at remote locations for subsequent playback by the main video tape recorder and, thus, would not require playback circuitry. In order to produce such an integrated camera/recorder, the mechanical aspects of the video tape recorder must be substantially miniaturized, in relation to the recorder used in the main playback and record unit. One of the critical features of such miniaturization is that the tape guide drum and the head mechanism in the tape guide path must be made substantially smaller than in the typical non-portable video tape recorder intended for home use, and this requires reducing the diameter of the tape guide drum. Nevertheless, simply reducing the diameter of the tape guide drum results in a pattern of tracks on the magnetic tape that does not coincide with the track pattern produced by a standard video tape recorder, and this presents problems during reproduction because the tape is to be played back using a standard diameter tape guide drum. The video track length, angle, and pitch have been standardized among all video tape recorders using the same format.
One approach to having the portable television camera recorder produce the same pattern of video tracks on the magnetic tape when using a substantially smaller diameter drum than standard is to wrap the magnetic tape around the drum for a larger circumferential extent (greater wrap angle) than that used in the conventional video tape recorder. The greater wrap angle in relation to the smaller diameter tape guide drum will provide an equivalent length of time for the head to contact the tape, thus, permitting a track of the same length to be laid down, but if the two heads remain spaced apart by 180.degree., then there will be a substantial time period before the second head is in position to commence recording after the first head has laid down its track. This relatively long time delay between tracks is to be avoided. One apparent approach to dealing with an increased wrap angle would be to scan the video tape with a single head, however, to record a video signal with the presently required high density it is necessary that the parallel tracks be formed abutting one another, with no space or guard band in between. This close arrangement of the tracks results in crosstalk during playback, and the best way of eliminating such crosstalk is to use two recording/playback heads with different azimuth gap angles. In this way, the azimuth loss of the reproduced crosstalk signal will render the adverse effects of such crosstalk signal insignificant. Thus, two heads are necessary to successfully record a video signal with high density. An ideal approach to this requirement would be to use two heads, both arranged at the same location, but since there must be some finite distance between the heads this prevents use of this ideal solution to the problem.
In typical color video cameras that are intended to cooperate with a video tape recorder, the output signal of the color video camera is encoded into a composite color video signal, and at the time it is to be recorded by the video tape recorder this composite color video signal is separated into a luminance signal and a color carrier (chrominance) signal. Typically, the luminance signal is FM modulated, and the color carrier signal is frequency down-converted to a frequency that is lower than the lower carrier frequency of the composite signal. Thus, to obtain the required video signal an encoder is required and a substantial amount of filtering and frequency conversion is also necessary to obtain the appropriate signal. All of this filtering and frequency converting deteriorates the frequency and phase characteristics of the color signal and results in degraded signal quality, as well as the side effect of producing spurious signals.